1. Field of the Invention
The invention relates to methods and compositions for controlling fluid loss in drilling fluids in which oil is the continuous phase and more particularly relates to the use of substituted-ammonium humates to control the fluid loss.
2. Brief Description of the Prior Art
Drilling fluids in which oil is the continuous phase are used for drilling oil wells which cannot be effectively drilled with water-based drilling fluids, because of such problems as the sloughing of clays, gelation at high temperatures, and the effects of contamination (by salt, gypsum, cement) resulting in high-viscosity, gelation and high fluid loss. The nature of emulsion muds and their use to minimize these problems have been described by Simpson, et al. (J. Pet. Tech., Dec. 1961, page 1177).
Invert emulsion drilling fluids result from the blending of an oil (typically diesel oil) with water in the presence of a suitable emulsifier. Oleophilic clays are used in these drilling fluids for increased stability, reduced water wetting, development of gel strength and reduced fluid loss. Additional fluid loss control is desirable and can be obtained by the use of organic filtration control additives (Simpson et al., supra.).
A known organic filtration control additive for oil muds consists of quaternary ammonium leonardites made by reaction of leonardite (or "lignite") with long chain quaternary alkylammonium compounds (Gray et al., composition and properties of oil well drilling fluids, 4th Edition, Gulf Pub. Co., Houston, Texas, (1980) page 66). Such agents are also described in U.S. Pat. Nos. 3,168,475 and 3,281,458.
Heretofore, a wide variety of drilling fluid additives have been proposed for oil muds. Included in the list of such additives are humates, lignitic materials and a wide variety of derivatives. Representative of such additives are those described in, for example, U.S. Pat. Nos. 3,168,475; 3,281,458; 3,379,650; 3,494,865; 3,775,447; 4,235,727; 4,311,600; and 4,421,655. In spite of the wide variety of drilling mud additives, a need has remained for additives which will improve fluid loss control.
We have now found that substituted-ammonium humates prepared from a particular humate material are exceptionally effective additives for fluid loss control in oil muds.